Untersuchungen zur Herstellung von Keramikfolien mittels Extrusionsgiessen Schlussbericht

For decreasing both the tendency to segregation and the drying time of typical ceramic slips in the doctor-blade-process high-solid aqueous alumina slips were moulded in a lab scale to thin layers and tapes, resp., by means of a slit extruder. The homogeneous deaerated bodies with a solid content up to 70% w (37% vol) using hydroxyethylcellulose as binder were mixed in a vacuum dissolver to a reproducible viscosity. The shaping of the wet layers was made by means of a plunger extruder by variation of the volume flow, the gap height, and the mode of applying the formed layer onto the support belt. Only in a drawing mode the thickness of wet layers corresponded with the width of the slit forming tapes from 0,13 to 0,60 mm thickness. In the bead mode almost the thickness of the layers was independent of the conditions of extrusion, but seemed to depend on the wetting and rheological properties of the casting bodies. The workability of the pseudoplastic bodies was limited by the pressure characteristic of the extruder and by the homogenization process. Due to the expensive facilities relating to the doctor-blade-process the application of slip extrusion for making thin ceramic tapes should be restricted to the moduling of complicated bodies or of multilayer tapes by a simultaneous wet-in-wet-deposition of the extruded single layers. (orig.)SIGLEAvailable from TIB Hannover: F96B1473+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman

Influence of temperature and aggressive solutions in the formation of thaumasite and ettringite in standard and commercial mortars

Formation of thaumasite or ettringite is depending on the temperature and the presence of carbonates, apart from the sulphate concentration. Although in the field exposition, these conditions may vary during the service life. In addition, not always is possible to control the composition of the commercial mortars or concretes. In the present work, seven different mortars are studied under two temperatures and three external solutions. The temperatures are 5 ºC and 20 °C. The solutions are water, sodium sulphate and sodium sulphate plus calcium carbonate. The aggregates are calcareous in the commercial mortars, and calcium carbonate, quartz and opal plus quartz in the standard mortars. The aspect, expansion and weight variation are analysed with time. The mortars with alkali reactive aggregates (opal plus quartz) show alteration under all conditions with variable damage. On the other hand, the expansion and the formation of thaumasite or ettringite is favored by low temperature and solution combination.Peer reviewe